title: Differential activation of cultured neonatal cardiomyocytes by plasmalemmal versus intracellular G protein-coupled receptor 55.
abstract: The L-α-lysophosphatidylinositol (LPI)-sensitive receptor GPR55 is coupled to Ca(2+) signaling. Low levels of GPR55 expression in the heart have been reported. Similar to other G protein-coupled receptors involved in cardiac function, GPR55 may be expressed both at the sarcolemma and intracellularly. Thus, to explore the role of GPR55 in cardiomyocytes, we used calcium and voltage imaging and extracellular administration or intracellular microinjection of GPR55 ligands. We provide the first evidence that, in cultured neonatal ventricular myocytes, LPI triggers distinct signaling pathways via GPR55, depending on receptor localization. GPR55 activation at the sarcolemma elicits, on one hand, Ca(2+) entry via L-type Ca(2+) channels and, on the other, inositol 1,4,5-trisphosphate-dependent Ca(2+) release. The latter signal is further amplified by Ca(2+)-induced Ca(2+) release via ryanodine receptors. Conversely, activation of GPR55 at the membrane of intracellular organelles promotes Ca(2+) release from acidic-like Ca(2+) stores via the endolysosomal NAADP-sensitive two-pore channels. This response is similarly enhanced by Ca(2+)-induced Ca(2+) release via ryanodine receptors. Extracellularly applied LPI produces Ca(2+)-independent membrane depolarization, whereas the Ca(2+) signal induced by intracellular microinjection of LPI converges to hyperpolarization of the sarcolemma. Collectively, our findings point to GPR55 as a novel G protein-coupled receptor regulating cardiac function at two cellular sites. This work may serve as a platform for future studies exploring the potential of GPR55 as a therapeutic target in cardiac disorders.
authors.affiliation: Center for Translational Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: Justine
authors.initials: J
authors.lastname: Yu
authors.forename: Elena
authors.initials: E
authors.lastname: Deliu
authors.forename: Xue-Quian
authors.initials: XQ
authors.lastname: Zhang
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Hoffman
authors.forename: Rhonda L
authors.initials: RL
authors.lastname: Carter
authors.forename: Laurel A
authors.initials: LA
authors.lastname: Grisanti
authors.forename: G Cristina
authors.initials: GC
authors.lastname: Brailoiu
authors.forename: Muniswamy
authors.initials: M
authors.lastname: Madesh
authors.forename: Joseph Y
authors.initials: JY
authors.lastname: Cheung
authors.forename: Thomas
authors.initials: T
authors.lastname: Force
authors.forename: Mary E
authors.initials: ME
authors.lastname: Abood
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koch
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Tilley
authors.forename: Eugen
authors.initials: E
authors.lastname: Brailoiu
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D032383:Myocytes, Cardiac / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043882:Receptors, Cannabinoid / Q000502:physiology*; D043562:Receptors, G-Protein-Coupled / Q000502:physiology*
chemical_list: C568825:GPR55 protein, rat; D043882:Receptors, Cannabinoid; D043562:Receptors, G-Protein-Coupled
keywords: Calcium Imaging; Calcium Intracellular Release; G Protein-coupled Receptors (GPCR); Heart; Intracellular GPCR; Intracellular Microinjection; Lysosomes; Membrane Potential; Ventricular Cardiomyocytes